(a) Field of the Invention
The present invention relates to a touch switch for controlling accessory equipment of a vehicle according to changes in electrostatic capacity caused when touched by a person.
(b) Description of the Prior Art(s)
Generally, an inner-door panel of a vehicle has a door pocket in which items such as a map are kept by an occupant in the vehicle. It is somewhat difficult to take out an item from the door pocket because light does not fully reach into the door pocket interior. Therefore, a door pocket provided with a lamp, which can be turned on/off with a touch switch, is used extensively therein. FIG. 8 shows the structure of a door pocket according to related technology.
The door pocket is comprised of mutually opposed side walls 10A and 10B, a main wall 10C which is connected to the side walls 10A and 10B to form a U-shaped wall, and a bottom plate 10D which makes the bottom of the door pocket. The door pocket is fitted to an interior panel 12 such that an opening on the opposite side of the main wall 10C comes in contact with the door interior panel 12. A lamp 14 is attached to the inside surface of the side wall 10A of the door pocket. A touch plate 16 which configures a vehicle accessory touch switch is fixed to the inside surface of the main wall 10C of the door pocket. When the touch plate 16 is touched by a person's hand to turn on the vehicle accessory touch switch, the lamp 14 is supplied with power and turned on.
By configuring as described above, the lamp 14 can be turned on when the occupant in the vehicle puts their hand into the door pocket to touch the touch plate 16. Thus, the occupant can easily take out an item housed in the door pocket.
FIG. 9 shows a structure of a vehicle accessory touch switch 18 according to a related technology applied to a door pocket. The touch plate 16 is formed of a dielectric material such as a synthetic resin or the like. A conductor plate 20 is joined to one surface of the touch plate 16. The conductor plate 20 is connected to a capacity measurement/control unit 24. The capacity measurement/control unit 24 is connected to a ground conductor 26 having electric potential as reference.
A switch 28 is controlled to be in an ON or OFF state by the capacity measurement/control unit 24. One of the terminals of the switch 28 is connected to a negative terminal of a battery 30. The other terminal of the switch 28 is connected to one of the terminals of the lamp 14. The other terminal of the lamp 14 is connected to the positive terminal of the battery 30.
The capacity measurement/control unit 24 measures electrostatic capacity between the conductor plate 20 and the ground conductor 26, and controls the switch 28 if the measured value has a change which exceeds a prescribed threshold value.
According to the configuration as described above, the electrostatic capacity between the conductor plate 20 and the ground conductor 26 can be varied when a surface on the other side of the touch plate 16 having the conductor plate 20 bonded is touched by a person's hand having electrostatic capacity with respect to the ground conductor 26. Thus, lighting of the lamp 14 can be controlled by touching the touch plate 16 with a hand.
The electrostatic capacity between the conductor plate 20 and the ground conductor 26 varies depending on humidity or the like of air around the vehicle accessory touch switch 18. Therefore, the vehicle accessory touch switch 18 might suffer from a malfunction because the capacity measurement/control unit 24 controls the switch 28 even when the electrostatic capacity is varied due to a change in the state of the surrounding air. Also, a noise voltage is induced in the conductor plate 20 by an unnecessary electromagnetic wave generated by other electrical equipment, and an error occurs in the electrostatic capacity measured by the capacity measurement/control unit 24, possibly causing a malfunction of the vehicle accessory touch switch 18.
The present invention has been achieved in view of the above-noted problems. Specifically, an object of the invention is to provide a touch switch for controlling accessory equipment of a vehicle so that a malfunction which may be caused by factors such as a change in the environment, like as a change of state of the air, arrival of unnecessary electromagnetic waves, or the like, can be avoided.